Two-stage roots type compressor

ABSTRACT

An improved two-stage Roots type compressor having a simplified construction which minimizes the number of hermetically sealed joints, characterized by a sandwich structure of first and second stage housings separated by a partition and surrounded by a spaced casing to provide a space which establishes communication between the discharge of the first stage and an inlet of the second stage, such casing having hermetically sealed joints only with remote ends of said housings.

O United States Patent 1191 1111 3,922,1 17

Weatherston 1 Nov. 25, 1975 1 TWO-STAGE ROOTS TYPE COMPRESSOR 1,531,607 3/1925 Green 418/9 3 9l. 3 l 1 .r 3 [75] Inventor: Roger C. Weatherston, 85 6/ 965 Kroeter 418/1 Williamsville, NY. FOREIGN PATENTS OR APPLICATIONS 73 Assignee; c l Corporation, B ff l 660,528 2/[929 France 418/9 [22] Flled: 1974 Primary Examiner-John J. V rablik [21] Appl. No.: 459,521 Altorney, Agent, or Firm-Allen J. Jaffe Related US. Application Data [62] Division of Ser. NO. 305,411, Nov. 10, 1972, ABSTRACT abandoned An improved two-stage Roots type compressor having a simplified construction which minimizes the number 32 of hermetically sealed joints, characterized by a sand F04C 17/10 FOlC wich structure of first and Second stage housings sepa- [58] Id f S h 8/5 9 13 rated by a partition and surrounded by a spaced casing le 0 earc to provide a space which establishes communication between the discharge of the first stage and an inlet of the second stage, such casing having hermetically [56] uNlTE lg g rz r s giqrENTs sealed joints only with remote ends of said housings. 1,238,501 8/1917 Ernst 418/11 3 Claims, 6 Drawing Figures us. Patant N0v.25,1975 Sheath 3,922,117

TWO-STAGE ROOTS TYPE COMPRESSOR This is a division of application Ser. No. 305,41 I, filed Nov. 10, I972, now abandoned.

BACKGROUND OF THE INVENTION Two-stage Roots type compressors of the prior art, as exemplified by the one disclosed in US. Pat. No. 3,667,874, for example, had a sandwich structure in which the first and second stage housings were formed by end plates, an intermediate partition, and enclosure for one stage arranged between one end plate and the partition, and another enclosure for the other stage arranged between the other end plate and the partition, hermetically sealed joints being required between the end plates and enclosures and between these enclosures and the partition. To provide such joints, machining of the mating surfaces was required which added to the expense of manufacture and assembly of the com pressor.

SUMMARY OF THE INVENTION 1 The present invention relates to an improved twostage Roots type compressor which also has a sandwich structure but in which the number of hermetically sealed joints is reduced, therebysimplifying the construction and reducing the machining of components for the compressor.

Another important advantage of the present invention is to provide such an improved two-stage Roots type compressor havingnot only the aforementioned features but also one which, for a given pitch diameter and operational speed, additionally can be reduced in size for handling the same inlet 'volume of gas. I

The present invention also provides a compressor for use in a refrigeration cycle, which, as compared to a compressor of the reciprocatingtype having a capacity of at least -20 tons, has the advantages of being more compact, simpler, provides at least equal performance, is lighter in weight, is less expensive and easier to manufacture as to components and is easier to assemble.

In accordance with the present invention, an. improved two-stage Roots type compressor is provided which comprises a first stage housing defining a first interior working chamber, a secondstage housing adjacent said first stage housing defining a second working chamber, a partition intermediate said first and second stage housings, a first stage inlet and outlet communi-.

eating with said first working chamber, a second stage inlet and outlet communicating with said second work- FIG. 3 is a vertical transverse sectional view of the first stage of said compressor taken on line 33 of FIG. 1.

FIG. 4 is a vertical transverse sectional view of the second stage of said compressor taken on line '4-4 of FIG. 1.

FIG. 5 is a fragmentary vertical central longitudinal sectional view of a compressor embodying a modified form of the present invention, the first and second stage portions of the compressor being shown partly in section and partly in elevation.

FIG. 6 is a vertical transverse sectional view of the second stage of the modified form of the invention, this view being taken on line 6-6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. l-4

Referring to FIGS. 1 through 4, the improved twostage Roots type compressor embodying one form of the present invention is shown as comprising a first stage housing 10 including an end plate 11 and an annular enclosure 12, a second stage housing 13 including an end plate 14 and an annular enclosure 15, and a partition 16 arranged intermediate these enclosures. These end plates, enclosures and partition are shown clamped together in sandwich arrangement by an annular series of tie bolts 18 severally having their corresponding ends threadedly secured in end plate 11 and their other ends severally carrying nuts 19 which press against the external end surface of the other end plate 14.

End plate ll, partition 16 and intermediate enclosure 12 jointly define a first stage interior working chamber' 20 (FIG. 3). End plate 14, partition 16 and intermediate enclosure 15 jointly define a second stage interior working chamber 21 (FIG. 4). A pair of rotary coacting multilobed impellers 22 and 23 is shown arranged in first stage working 'chamber 20. A similar pair of impellers 24 and 25 is shown arranged in second stage working chamber 21.

End plates 11 and 14 are shown as having laterally outwardly extending or external coaxially aligned tubular necks 27 and 28, respectively. Bearings in these ing chamber, and a casing over said first and second housings to provide a space establishing communication between said first stage outlet and second stage inlet.

Other objects and advantages of the present invention will be apparent from the following detailed description of preferred embodimentsthereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 2 is a horizontal central longitudinal sectional I view thereof taken on line 2-2 of FIG. 1

necks receive a shaft 29 which is journaled thereon and extends through end plates 11 and 14 and partition 16. End plates 11 and 14 are also shown as provided with a second 'set of similar tubular necks 30 and 31, respectively', having coaxially alined bores severally provided with suitable bearings to receive a second shaft 32 which is journaled thereon. At their corresponding ends, shafts 29 and 32 are shown as provided with a pair of meshed gears 33 and 34, respectively, severally fast to these shafts. These gears are arranged externally of end plate 14 or on the side thereof opposite from enclosure 15. The opposite end of shaft 29 is shown as extended to constitute or be suitably joined to the rotor of an electric motor 35 of suitable construction, the stator of which is suitably supported on neck 27. This motor 35 rotates shaft 29, and through gears 33 and 34 the other shaft 32 is rotated in an opposite direction and timed relation.

Suitably nonrotatively mounted on shafts 29 and 32 are first stage impellers 23 and 22, respectively, as are second stage impellers 25 and 24, respectively.

Surrounding motor 35 and in spaced relation thereto 1 is a compressor inlet casing 36 of generally cup-shaped form having a cylindrical side wall 37, an end wall 38 provided with a central inlet 39 in its otherwise closed end wall 39, and an outwardly extending annular attaching flange 40 at its opposite end. This flange has a flat end face 41 which abuts the opposing flat end face 42 of end plate 11. An annular series of removable fasteners such as screws 43 are shown as securing attaching flange 40 to end plate 11. End face 41 of this flange is shown as provided with an annular groove 44 to receive an annular seal ring such as an O-ring 45 made of elastomeric material. The exposed face of this O-ring compressively engages the opposing face 42 of end plate 11 and provides a continuous annular seal between the flange and end plate.

A compressor outlet casing 46 is shown as having a cylindrical side wall 47, an end wall 48 at its outer end and an outwardly extending annular attaching flange 49 at its inner end. Side wall 47 surrounds end plate 14 and partition 16 and is in spaced relation to enclosures 12 and 15, thereby providing an annular space 50. This casing is also of generally cup-shaped form having a radially offset compressor outlet 51 in its closed end wall 48. Attaching flange 49 has a flat end face 52 abuttingly engaging the opposing flat end face 53 of end plate 11. An annular series of fasteners such as screws 54 are shown as securing this attaching flange 49 to end plate 11. End face 52 of this attaching flange is shown as provided with an annular groove 55 in which an annular seal ring such as an elastomeric O-ring 56 is arranged, the exposed portion of this O-ring compressively engaging the opposing end face 53 of end plate 11 to provide an effective annular seal.

End plates 11 and 14 are circular in outline as viewed from the end. End plate 14 is shown as being of smaller diameter than end plate 11 and has a cylindrical periphery 58 adapted to oppose in closely spaced relation the inner surface of cylindrical casing side wall 47. This periphery 58 of end plate 14 is shown as provided with an annular groove 59 in which a continuous annular seal ring such as an elastomeric O-ring 60 is arranged, an, exposed portion of this O-ring being compressed against the opposing inner surface of casing side wall 47. I

End plate 11 is shown as having an opening 61 therethrough which serves as the axial inlet for the first stage working chamber 20 and communicates with the interior of compressor inlet casing36 and its inlet 39. The

a similar pair of ledges 74 and 75 adjacent outlet opening 64. The latter ledges also preferably severally have feedback passages 76 for the same purposes disclosed in said patent.

From the foregoing. it will be seen that with electric motor 35 energized and driving the impellers 22-25 of the two-stage compressor, low pressure gas is drawn through compressor inlet 39, flows around this motor and enters the first stage working chamber 20 through the inlet opening 61. In such working chamber the gas is compressed and discharged through outlet opening 62 into annular space 50. This intermediately pressurized gas in space now flows through inlet opening 63 for the second stage working chamber 21 wherein it is compressed to a higher pressure and discharged through outlet opening 64 and tube 65 to a point external of the compressor.

An important feature of the present invention is the simplicity of the structure providing the first and second stages. It will be seen that the compressor outlet casing 46 being in spaced relation to enclosures l2 and 15 of the two compressor stages provides the space 50 which establishes communication between the first stage discharge and the second stage inlet. This arrangement requires only the provision of a pair of seals such as provided by O-rings 45 and between end plates 11, 14 and the compressor outlet casing 46. In addition, there is only a single seal required between the compressor inlet casing and end plate.

FIGS. 5 & 6

In the modified form of the invention shown in FIGS. 5 and 6, the first stage of the compressor is similar to that disclosed for the form shown in FIGS. 1-4 except that the width or axial length of the working chamber is shorter in the modified form. Corresponding parts of the modified formare represented by the same numerals as applied in the first form except for the addition of a prime. Thus, the first stage of the modified form has an enclosure 12 having an outlet opening 62'. Partition 16' is shown as having an opening 78 extending axially therethrough-in general alignment with inlet openfirst stage enclosure 12 is shown ashaving a radial outlet opening 62 which establishes communication between the working chamber 20 of this first stage and annular space 50. The second stage is shown as having a radial inlet opening 63 arranged in the wall of enclosure 15, and this opening establishes communication between space 50 and the second stage working chamber 21. End plate 14 is shown as having an axial outlet opening 64 for the second stage working chamber 21. A tube arranged in this outlet opening 64 and in the compressor outlet opening 51 conducts the discharge of the second stage to this compressor outlet.

Referring to FIG. 3, the first stage working chamber 20 is shown as defined in part by a pair of ledges 67 and 68 adjacent inlet opening 61. A similar pair of ledges 69 and 70 is shown arranged adjacent outlet opening 62. Preferably, each of these latter ledges has a feedback passage 71 for the purpose disclosed in US. Pat. No. 3,531,227.

Similarly, as shown in FIG. 4, the working chamber 21 for the second stage of the compressor includes a pair of ledges 72 and 73 adjacent inlet opening 63, and

ing 61 in end plate 11' so as to establish communication between the inlets for the working chambers of the two stages.

The enclosure1l5'- for the second stage does not have an inlet corresponding to the one shown at 63 in the first form. In this modified form, the inlet for the second stage is the opening 78 in intermediate partition 16.

The salient portions of the lobes of the impellers 24 and 25' of the second stage severally have a wiping contact ,with the surrounding partially cylindrical wall surface portions 79 and 80, respectively. of the second stage working chamber 21'. Referring to FIG. 6, it will be seen that between two adjacent lobes on impeller 24' having such wiping contact jointly with the surrounding workingchamber wall surface 80 provides a closed volu me well 81. Another closed volume well 82 is provided jointly by two adjacent lobes on the other impeller 25 jointly with wall surface 79. An inlet passage is shown as arranged in enclosure 15' on each side thereof so as to establish communication between annular space 50' and the wells 81 and 82, such passage for well 81 being indicated at 83 and that for well 82 at 84.

In operation, the form of the invention shown in FIGS'. 5 and 6 receives its low pressure gas through inlet opening 61' in end plate 11, some of which gas is handled in the working chamber 20 of the first stage and the balance of the gas passing through opening 78 in intermediate partition 16' and being handled by the second stage working chamber 21. The partially compressed gas discharged through outlet opening 62' from the first stage enters annular space 50' and from this space flows inwardly through inlet passages 83 and 84 into wells 81 and 82. This adds to the mass of gas in these wells and represents additional gas which can be compressed without additional work input. The gas compressed to a high pressure leaves outlet opening 64' and is conducted by tube 65' to a point external of the compressor.

A feature of the modified form of the invention is that the axial length of the housings and 13' forming the two stages of the compressor can be foreshortened as compared to the housings l0 and 13 employed in the first form, assuming the same pitch diameter for the impellers and that they are rotating at the same angular speed. The axial length of enclosure 12' added to that of enclosure 15' is equivalent to the axial length of enclosure 12 in the first form of the invention.

Although two preferred embodiments of the present invention have been described, changes will occur to those skilled in the art; therefore, it is intended that the scope of the present invention is to be limited only by the scope of the appended claims.

What is claimed is:

1. In a multi-stage Roots type compressor, comprising a first stage housing defining a first interior working chamber, a second stage housing adjacent said first stage housing defining a second interior working chamber, a pair of rotary coacting multilobed impellers arranged in each of said first and second working chambers and severally with said first and second stage housings providing closed well volumes, a first inlet and outlet communicating with said first working chamber, a second inlet and outlet communicating with said second working chamber, means providing communication between said first outlet and said secondstage closed well volumes, and means providing communication between said first and second inlet.

2. In a multi-stage Roots type compressor, comprising a first stage housing defining a first interior working chamber, a second stage housing adjacent said first stage housing defining a second interior working chamber, a partition intermediate said first and second stage housings, a first inlet, and outlet communicating with said first working chamber, a second inlet and outlet communicating with said second working chamber, a casing over said first and second housings to provide a space establishing communication between said first outlet and said second interior working chamber, said first stage housing includes a first end plate and a first enclosure, said second stage housing includes a second end plate and a second enclosure, said partition being arranged between said first and second enclosures, said casing surrounds said second end plate and partition and is arranged in spaced relation to said first and second enclosures to provide said space, said first inlet being in said first end plate, said first outlet being in said first enclosure and communicating with said space, said second inlet being in said partition and communicating with said first inlet, said second outlet being in said second end plate, said compressor further comprising a pair of rotary coacting multilobed impellers arranged in each of said first and second working chambers and severally with said first and second stage housings providing closed volume wells and said second enclosure having an inlet passage establishing communication between said space and each of said closed volume wells for the second stage.

3. In a multi-stage Roots type compressor, comprising a first stage housing defining a first interior working chamber, a second stage housing adjacent said first stage housing defining a second interior working chamber, a partition intermediate said first and second stage housings, a first inlet and outlet communicating with said first working chamber, a second inlet and outlet communicating with said first working chamber, a second inlet and outlet communicating with said second working chamber, a casing over said first and second housings to provide a space establishing communication between said first outlet and said second interior working chamber, said first stage housing includes a first end plate, said second stage housing includes a second end plate, said casing is arranged on one side of said first end plate and secured thereto, and surrounds said second end plate and partition, and which further comprises a compressor inlet casing arranged on the other side of said first end plate and secured thereto and an outlet casing, said compressor inlet casing having a compressor inlet, said compressor outlet casing having compressor outlet, said first inlet being in said first end plate and communicating with said compressor inlet, and said second outlet being in said second end plate and communicating with said compressor outlet, said first stage housing includes a first enclosure, said second stage includes a second enclosure, said compressor outlet casing is arranged in spaced relation to said first and second enclosures to provide a space, said first outlet being in said first enclosure and communicating with said space, said second inlet being in said partition and communicating with said first inlet, said compressor further comprising a pair of rotary coacting multilobed impellers arranged in each of said first and second working chambers and severally with said first and second housings providing closed volume wells, and said second enclosure having an inlet passage establishing communication between said space and each of said closed volume wells for the second stage. 

1. In a multi-stagE Roots type compressor, comprising a first stage housing defining a first interior working chamber, a second stage housing adjacent said first stage housing defining a second interior working chamber, a pair of rotary coacting multilobed impellers arranged in each of said first and second working chambers and severally with said first and second stage housings providing closed well volumes, a first inlet and outlet communicating with said first working chamber, a second inlet and outlet communicating with said second working chamber, means providing communication between said first outlet and said second stage closed well volumes, and means providing communication between said first and second inlet.
 2. In a multi-stage Roots type compressor, comprising a first stage housing defining a first interior working chamber, a second stage housing adjacent said first stage housing defining a second interior working chamber, a partition intermediate said first and second stage housings, a first inlet, and outlet communicating with said first working chamber, a second inlet and outlet communicating with said second working chamber, a casing over said first and second housings to provide a space establishing communication between said first outlet and said second interior working chamber, said first stage housing includes a first end plate and a first enclosure, said second stage housing includes a second end plate and a second enclosure, said partition being arranged between said first and second enclosures, said casing surrounds said second end plate and partition and is arranged in spaced relation to said first and second enclosures to provide said space, said first inlet being in said first end plate, said first outlet being in said first enclosure and communicating with said space, said second inlet being in said partition and communicating with said first inlet, said second outlet being in said second end plate, said compressor further comprising a pair of rotary coacting multilobed impellers arranged in each of said first and second working chambers and severally with said first and second stage housings providing closed volume wells and said second enclosure having an inlet passage establishing communication between said space and each of said closed volume wells for the second stage.
 3. In a multi-stage Roots type compressor, comprising a first stage housing defining a first interior working chamber, a second stage housing adjacent said first stage housing defining a second interior working chamber, a partition intermediate said first and second stage housings, a first inlet and outlet communicating with said first working chamber, a second inlet and outlet communicating with said first working chamber, a second inlet and outlet communicating with said second working chamber, a casing over said first and second housings to provide a space establishing communication between said first outlet and said second interior working chamber, said first stage housing includes a first end plate, said second stage housing includes a second end plate, said casing is arranged on one side of said first end plate and secured thereto, and surrounds said second end plate and partition, and which further comprises a compressor inlet casing arranged on the other side of said first end plate and secured thereto and an outlet casing, said compressor inlet casing having a compressor inlet, said compressor outlet casing having compressor outlet, said first inlet being in said first end plate and communicating with said compressor inlet, and said second outlet being in said second end plate and communicating with said compressor outlet, said first stage housing includes a first enclosure, said second stage includes a second enclosure, said compressor outlet casing is arranged in spaced relation to said first and second enclosures to provide a space, said first outlet being in said first enclosure and communicating with said space, said second inlet being in said partition and communIcating with said first inlet, said compressor further comprising a pair of rotary coacting multilobed impellers arranged in each of said first and second working chambers and severally with said first and second housings providing closed volume wells, and said second enclosure having an inlet passage establishing communication between said space and each of said closed volume wells for the second stage. 